Color filters are generally used in liquid crystal displays, optical filters of cameras, and the like. Color filters can be prepared by coating a minute area with three or more colors onto a solid state imaging device or a transparent substrate. Such colored thin films are typically formed by dyeing, printing, electrodeposition, pigment dispersion, ink-jet printing, and the like. Currently, such methods are applied to production of LCDs, such as those used in mobile phones, notebook computers, monitors, TVs, and the like.
In the dyeing method, a colored thin film may be produced by forming an image having a dyeing matrix, such as natural photosensitive resins like gelatin, amine modified polyvinyl alcohols, amine modified acrylic binder resins, and the like, on a glass substrate, followed by dyeing with direct dyes. In order to form a multi-colored thin film on the same substrate, it is necessary to perform flame retardant finishing whenever the color changes, thereby complicating the production process and delaying production time. Although general dyes and resins per se have good clarity and dispersibility, these dyes and resins have drawbacks in that they have poor light resistance, moisture resistance, and heat resistance, which is the most important property.
In the printing method, a colored thin film may be produced by printing an ink wherein a pigment is dispersed in a thermosetting or photocurable resin, followed by curing these components with heat or light. This method may reduce material costs as compared to other methods. However, the method has drawbacks in that it is difficult to form a highly defined and minute image, and the formed thin layers are not uniform.
Korean Patent Publication No. 1996-0011513A discloses a method for producing a color filter by ink jet printing. However, this method can result in deteriorated durability and heat resistance like the dyeing method since a colored photosensitive resin composition to be injected from a nozzle to print a minute and defined color is prepared in dye form.
In the pigment dispersion method, a colored thin film is produced by repeating a series of steps including: coating a photopolymerizable composition containing a colorant on a transparent substrate on which a black matrix is provided, exposing the composition to light in a desired pattern, removing the unexposed portion with a solvent, and heat curing. The pigment dispersion method can enhance heat resistance and durability and can maintain the thickness of films uniformly.
As a pigment for a color filter in the pigment dispersion method, C.I. Pigment Green, C.I. Pigment Yellow, C.I. Pigment Blue, C.I. Pigment Violet, and the like essentially consisting of phthalocyanine pigments are used in combination. However, in this case, atomization of the pigments may limit luminance and contrast owing to pigment particle size. As a method for additionally improving color properties, it is necessary to introduce a highly durable dye having no particulate property in a molten state or a very small primary particle diameter of not more than several nanometers.
In general, although there has been extensive research directed to color filters including dyes, it is difficult to provide both excellent light transmission and excellent absorption capabilities in a desired color range. Further, dyes satisfying high contrast together with basic reliability for use in color filters are very rare.